Preheat the oven to 350 degrees F (177 degrees C) and place the rack in the center of the oven.

Graham Cracker Crust:  Mix together the graham cracker crumbs, sugar, and melted butter.   Press onto the bottom and up the sides of a well greased 9 inch (23 cm) pie or tart pan.  Cover with plastic wrap and place in the refrigerator to chill while you make the filling. 

Filling:  In the bowl of your electric mixer, with the whisk attachment, beat the egg yolks until pale and fluffy (about 3 minutes).  Gradually add the condensed milk and beat until you have a light and fluffy mixture (4-5 minutes).  Scrape down the sides of the bowl and beat in the lime juice and zest. 

Pour the filling into the crust and bake for about 10 minutes, or until the filling is set.  Remove from oven and place on a wire rack to cool.  Once it has completely cooled, cover and refrigerator until serving time.  (The pie can be made to this point and stored in the refrigerator for a couple of days.)  Just before serving make the whipping cream.

In a separate bowl, beat the whipping cream until soft peaks form.  Add the sugar and beat until stiff peaks form.  Either pipe or place mounds of whipping cream on top of the filling. 

Makes 1 - 9 inch (23 cm) pie or tart.